xv. FROGGIES. 210 



These animals are indeed obliged to keep their mouths 

 shut, for if they kept them open they would riot be able 

 to breathe. It is possible to suffocate a frog by holding 

 his mouth open. The way frogs breathe is curious and 

 may readily be watched. The floor of the mouth, the 

 part that covers the under jaw, is during life in constant 

 motion, continually rising and falling; and if you watch 

 carefully you will see that two little holes, the nostrils, one 

 on each side of the snout, are constantly opening and closing. 

 At the back of the mouth there is a slit-like opening, 

 which you may readily see in a dead frog, and which leads 

 into the tube that passes to the lungs. The mouth is 

 thus a sort of bellows. Air is sucked in through the 

 nostrils and forced downwards into the lungs by the 

 bellows-like action of the floor of the mouth. This is 

 quite different from the way in which you breathe. If 

 you put your hands to your chest, you will feel your ribs 

 rising and falling as you breathe. They are part of the 

 mechanism of that beautiful suction-pump by which you 

 draw air into your lungs. The frog has no ribs, its sides 

 are quite limp ; and he has to use his mouth as a bellows 

 or force-pump to drive or force the air into his lungs. If 

 you hold his mouth open his bellows won't work, and you 

 suffocate him. His lung too is quite different from yours, 

 being a hollow bag, the sides of which have a sort of 

 honeycomb lining ; whereas yours are composed cf a 

 multitude of little tubes, with tiny air bladders at the 

 ends, packed as close as ever they can be. The frog also 

 breathes a great deal through his skin, which so long as 

 the creature is healthy is always moist. 



The skin has also the power of changing colour. If you 

 keep a frog in a dark place he will become quite pale and 

 sober coloured. But if you bring him out into the clear 

 sunlight, he will soon brighten up ; his spots and patches 



